1. Field of the Invention
The present invention relates generally to apparatus and methods of attaching and aligning weapons accessories such as an optical targeting or alignment system to a base. More particularly, certain embodiments pertain to apparatus and methods for attaching and aligning optical sighting systems to ballistic launchers. More specifically, an embodiment pertains to adjustable mounting systems for telescopic sights.
2. Discussion of Relevant Art
William Malcolm is credited with building the world's first production rifle scopes, in 1855. He was first to offer an adjustable ocular lens. His windage and elevation adjustable mounts moved the entire tube to align vertical and horizontal crossed hairs within the tube with the point of impact at a set selected distance. A limited number of recent products and patents in this area have addressed the assembly that connects the rifle to the telescopic sight. Most have involved the internal functions of the telescopic sight.
The modern tactical rifle scope is more than an evolutionary development. By any measure it is revolutionary. It may utilize as many as ten separate lenses in light's path from the objective (front) lens to the ocular (rear) lens. Crossed hairs have morphed into spider web and wire, then into etched glass. Fixed magnification power has yielded to amazing variable power magnification systems. The one challenge that presents itself as a constant, from the earliest developments until now, is the matter of reconciling point of aim with point of impact on either side of the one point on a bullet's ballistic arc where the shooter has “zeroed in his scope”. Cartridge makers have long published charts which show inches of drop at regular distances from the muzzle for each of their bullet-load combinations. The military has adopted Minutes Of Arc (MOA) for adjusting sights vertically to account for the effects of gravity on a bullet's trajectory.
Today's long distance shooter uses technology beyond the imagination of William Malcolm. For example, Knight's Armament offers a ballistic computer application for the ubiquitous Apple Ipod®. A user's selection of a bullet (or cartridge) from a database of a listed manufacturer's products offers a menu of various calibers and profiles. The user input of the range to target is combined with altitude derived from the Ipod's internal GPS. Other factors like temperature and barometric pressure are factored into the calculations for the distance a projectile will fall before striking a target. Advanced software can even consider the Coriolis Effect from the earth's rotation. Once the calculations are complete and all the factors are considered, the output from the device is displayed on the LCD screen in minutes of angle, the familiar MOA. The shooter simply twists the top dial (graduated in minutes of angle) as directed to shift the aiming point to reflect the amount the rifle's muzzle must be tilted upward to launch the bullet on a ballistic arc that will intersect with the line of sight at the exact range entered.
It is what happens inside the scope that is more often than not a bigger mystery than the Ipod computer functions. A tactical rifle scope contains many parts for what, on the surface, appears to be a fairly simple device. The three major parts of a telescopic sight are far more complex than the casual user might imagine. The heart of an MOA adjustable scope is an erector tube within the main barrel of the scope. A minutes of angle ratio and proportion can be concealed within the barrel of the scope. The up or down movement of a plunger at the rear of the erector tube divided by the distance between the erector tube's front pivot point and the plunger yields a very special number, the sine of the angle the erector tube is inclined from the barrel axis. That angle is expressed as the now-familiar “MOA.”
When the erector assembly is parallel to the main scope tube, (the “zero” or neutral position) the light's path through the scope is direct, symmetrical and free from distortion. It is only when the long range shooter begins twisting the adjustment knobs that the laws of physics conspire to compromise his hope for “one shot, one kill.” A socket machined at the front of the typical scope tube and a matching ball formed on the outside of the erector tube form a mechanical joint known as a trunnion. A spring fixed below the rear of the erector tube provides the return pressure acting against the force of a threaded stem that winds down with the user's twisting of the elevation adjustment.
The path of light through the scope now follows a much different route. As the erector assembly is tilted and the magnification lenses within the erector separate, the laws of refraction must be obeyed. Light projected onto the rear focal plane and the trailing lens is perpendicular to the axis of the rear magnification lens. The deflection angle produces angular distortion. The path of light is not along the centerline of the lens. The asymmetrical aspect through the rear lens creates refraction distortion. Thus, no matter how mechanically precisely the MOA adjustment compensation is introduced into the erector tube, the throughput is an optical approximation. Furthermore, another adjustment in the scope's objective lens assembly for parallax can reduce accuracy again.
Further distortion may be introduced into the erector tube with any serious adjustment for windage. Light that passes from lens to lens off center in both X and Y axes (i.e., horizontal and vertical) will result in spherical aberration as well.
The mechanism at the rear of the erector tube that tilts the assembly is vulnerable to damage or deterioration with repeated use. The spring on the opposite side of the adjustment screw and plunger tube provides the essential force required to return the tube to the neutral position or less than neutral for shots at less than the pre-set “zero” point. Since they are engineered for a limited number of duty cycles, every part in such systems will eventually wear out. Each erector tube assembly has a limited range of adjustment. A shooter working near the limits of the system's envelope is often tempted to squeeze one more minute of angle from the scope's limited range of motion. But if he over-torques the MOA knob, internal parts will fail. For a bench shooter competing for bragging rights at a 1,000 yard competition, scope failure is something that has happened to you before or will happen one day soon. See, e.g. the recent article “When Good Scopes Go Bad—Making the Difficult Diagnosis,” published Sep. 25, 2010 in ACCURATE SHOOTER, accessible online at http://bulletin.accurateshooter.com/2010/09/when-good-scopes-go-bad-making-the-difficult-diagnosis/. At best, this might be considered a minor inconvenience. At worst, the competitive shooter may watch someone else walk of with “his” prize. However, for the hunter or shooter engaged in combat, the stakes are much higher. The shooting community is rampant with anecdotal horror stories of telescopic sights failing in accordance with “Murphy's law” after repeated adjustments.
It is well known to provide mechanical means for adjusting the elevation of sighting and ranging devices mounted to a base. Aiming or sighting devices, laser target illumination devices and laser ranging devices are commonly mounted to ballistic projectile launchers, such as rifles, and to other apparatus requiring adjustment along a longitudinal axis. Common aiming or sighting devices include various types of telescopic optical scopes. Other aiming or sighting devices include telescopic and non-telescopic thermal imaging scopes and telescopic and non-telescopic amplified light imaging optical scopes.
Adjustable mounting systems are frequently used to mount telescopic scopes, and similar aiming devices, upon the barrels of rifles or similar firearms. The most common telescope sights are non-amplified, optical devices having front and rear mounting points. Such telescopic sights are typically attached by means of mounting systems to the barrels of rifles or similar weapons by means of a mounting system to the barrel of a rifle in a configuration having the rear sight of the scope adjacent to the rifle's breech and the front sight of the scope directed toward the muzzle. The scope's sighting axis is approximately aligned with the bore axis of the rifle and is adjusted vertically in elevation and adjusted laterally in windage such that the point of aim observed by the shooter is the point of impact of the projectile at the desired range. Other elevation and windage adjustments may be necessary based upon a number of well known factors in including wind speed and direction, temperature, humidity, projectile shape and mass, and powder mass and burn characteristics. Since projectiles follow a ballistic path, adjustments in elevation may be a critical factor or hitting targets at ranges approaching the maximum range of the particular cartridge-rifle combination.
The amounts of elevation adjustments needed for telescopic sights mounted on high powered sporting and military rifles frequently exceed the amounts of adjustment achievable by the elevation adjustment mechanisms within the telescopic sight itself. Furthermore, the internal adjustment mechanisms of most telescopic sights are less accurate over the outer limits of their adjustment ranges. The internal adjustment mechanisms are frequently positioned such that a shooter in the firing position cannot easily reach the controls and cannot readily read the adjustment markings. Additionally, the internal adjustment mechanisms of telescopic sights my be inadvertently displaced by the acceleration experienced during recoil and other shocks. Adjustable mounting systems are used to mount telescopic sights to provide for greater amounts of elevation adjustments and greater resistance to displacement of the elevation adjustment mechanisms during recoil or other shocks.
Some target shooters have employed tapered ramps, wedges or shims that fit between scope and rifle to externally adjust the elevation of the scope relative to the barrel without using the existing internal scope mechanisms. These wedge shapes are machined in increments of ten to twenty minutes of angle to extend the range of a scope beyond the manufacturer's upper limits of internal adjustment. However, for every yard added on the long end the shooter gives up three feet on the short side.
A very large part of exacting marksmanship is confidence in one's equipment. Function and endurance are the measure of each part of the total system. The Military has recognized the need for a more dependable, predictable and repeatable aiming system. The recently completed Defense Advanced Research Projects Agency (DARPA) program awarded Lockheed Martin a $3.93 million contract to develop a rifle-scope attachment to enhance soldiers' marksmanship capabilities. See the article, “DARPA's Self-Aiming ‘One Shot’ Sniper Rifle Scheduled for Next Year,” published by Popular Science on Oct. 1, 2010, accessible online at www.popsci.com/technology/article/2010-10/aiming-help-snipers-Lockheed-development . . . .
The Dynamic Image Gunsight Optic or DInGO system which is the objective of this project is hoped to enable soldiers to accurately view targets at varying distances without changing scopes or suffering a decrease in optical resolution. This system was recently reported on the Defence and Airospace news blog, accessible online at www.brahmand.com/news/Lockheed-receives-$393-min-DInGO-system-contract-from-darpa/4011/1/24.html. By the DARPA program's own definitions, the military is recognizing a problem exists—a problem they are willing to spend millions to solve. Much of what has been submitted in this competition is not yet public knowledge, but it is safe to assume that an industry invested in the existing MOA adjustable erector tube within the scope could not use an outside the box solution to the problem. More electronics and holographic reticles are not the answer. Many a soldier or bench shooter has made the observation and asked the question, “But what happens when the batteries go dead?” Keep it simple stupid, KISS for short is an apt maxim. It is safe to say that, “The concept of shifting the point of aim optically is flawed.”
Assorted prior art patents reveal a number of inventors who have attempted to create mounting system for scope to rifle that would provide a mechanism to create a deflection angle between the typical parallel alignment between rifle bore and scope line of sight. All start with the premise that the scope's windage and elevation adjustment systems should be reserved for the initial task to sight in or “zero” the aiming system at a pre-set distance. Some examples use ramps or wedges, while others employ cams. Dials marked with numbers or Vernier scales suggest a level of precision that is difficult to achieve across a wide range of cartridges and bullet weights.
International Publication WO 2008/099351 discloses a sight support for a projectile launcher having a first member to be attached to the launcher and a second member pivotally connected to the first member and arranged to support a sight, with a worm drive acting between the two members to pivot them toward and apart from one another.
U.S. Pat. No. 7,121,037 discloses an adjustable scope mounting device for adjusting a scope mounted on a gun, using opposite threaded screws for elevational adjustment. FIG. 2 shows an adjusting wheel with detents which contact a pin as part of the process of measuring the amount of elevational adjustment.
U.S. Pat. No. 3,990,155 discloses a riflescope elevation adjustment assembly which reads directly in terms of target distance in addition to providing “click” type elevation settings. An external adjustment knob is provided and a distance scale is displayed on an annular flange extending from the knob.
U.S. Pat. No. 7,690,145 discloses ballistic ranging methods for determining ballistic drop of shooting a projectile to a specific target range, using a laser rangefinder and ballistic software program.
Steven Ivey has a number of patents for adjustable rifle scope mounts His U.S. Pat. No. 7,140,143 discloses an adjustable elevation mount formed from a scope ring and an adjustable sub-base. A cylindrical elevation cam and a dial thimble are used as portions of the adjustment mechanism. U.S. Pat. No. 7,543,405 is a CIP of this patent disclosing several additional embodiments.
Leatherwood's U.S. Pat. No. 6,772,550 discloses a rifle scope adjustment mechanism using a pivot point and screw-driven tilting mechanism using a spring to move the scope upward. The system can be applied to the internal components of the scope or to an external mount.
Major ammunition manufacturers have published charts that describe their product's ballistic characteristics. See, for example, the data for Remington's popular 308 round in Table I below. Note the difference in bullet drop at 500 yards between the various factory loads.
TABLE IREMINGTON BALLISTICS CHARTCartridge100 150 200 300 400 TypeBulletydsydsydsydsydsRemington125+1.1″Zero−2.7″−7.4″−38.5″ManagedRecoilPremier150+1.8″+1.6″Zero−3.1″−22.7″SirrocoBondedPremier180+1.9″+1.7″Zero−3.4″−25.5″Core-LoktUltra(This data was obtained from Remington Arms website, www.remington.com/pges/news-and-resources/ballistics.aspx.)
While this information is helpful, it is just the starting point. The distance between the scope's line of sight and the rifle's bore sight is the first variable to consider. That distance must be added to the inches of drop at a given range to calculate the angle between that point out in space and the scope's line of sight. For example: a rifle scope with high mount scope bases might rise about 2.4″ above the centerline of the barrel. When added to the drop published for the 168 gr Express cartridge of 78.2,″ the point of aim must be raised a total of 80.6″ to impact the target at the required distance of 500 yards. The drop of 80.6″ divided by (500 yds×3′×12″) is equal to 0.004488 or the sine of zero degrees, 15 minutes and 24 seconds. Armed with only the published data, anyone with a hand held trig function calculator and a range finder who could put “the dope on the scope” could put a projectile on the target. He could, if it weren't for those problems with refraction distortion, angular distortion and parallax error and if his scope had enough adjustment left after he zeroed it in at 100 yards. That would be a problem. That is why the adjustable scope base disclosed herein is invaluable. For 15¾ MOA, one need only twist the dial a half revolution plus three clicks.
Selected MOA values required for selected cartridges at various ranges are presented below in Table II. Note that at 1000 yards, the required MOA adjustments exceed the internal adjustment capabilities of conventional optical scopes and mechanical systems such as disclosed in Ivey's U.S. Pat. No. 7,543,405.
TABLE IILine of sight above line of bore = 3.00 inchesAdjust minutes of angle for point of aim - to point of impactCartridge 100 200 400 500 1000TypeBulletydsydsydsydsydsRemington125Zero3¼ moa9½ moa14¼ moa37½ moaManagedRecoilPremier150Zero2¼ moa6½ moa9½ moa34½ moaSirrocoBondedPremier180Zero2½ moa7½ moa11¾ moa72¾ moaCore-LoktUltra(Data in this table were calculated by Applicant from Sierra Bullets, a Sierra Ballistics program.)
Despite numerous efforts to provide external adjustments in the relationship of telescopic sights with relation to the boresights or similar axes of ballistic weapons launchers in elevation and/or windage (lateral movement), as evidenced by patents including those discussed above, there remains a need for a simple, rugged and reliable adjustable base for securing such sights to rifles and the like.